Hot-melt adhesive compositions are typically solid at room temperature. Therefore, said adhesive compositions are heated and are subsequently applied to a substrate in a molten state, which is then placed in contact with one or more further substrates. The hot-melt adhesive composition cools and solidifies, thereby forming a bond between the substrates.
Hot-melt adhesive compositions can be used for a variety of industrial adhesive applications such as packaging and labeling, production of nonwoven hygiene and sanitary articles, such as for the bonding of elastics, construction and core lamination or positioning adhesive and also for other laminates such as tapes and labels.
To prevent hot-melt adhesive compositions from agglomerating prior to their intended use, said adhesive compositions are typically provided in a packaged form. Packaged hot-melt adhesives are typically composed of a base polymer, a tackifying agent and a wax component. The base polymer provides the formulation with its strength and adhesive characteristics. The tackifying agent allows the polymer to be more adhesive by improving wetting during the application, and give tack to the adhesive and also lower the viscosity. Tack is required in most adhesive formulations to allow for proper joining of articles prior to the hot-melt adhesive solidifying.
A great disadvantage of currently used packaged hot-melt pressure sensitive adhesives is that fusion of the several packaging materials increasingly leads to agglomeration of several particular forms during storage, which may lead to the blocking of said individual forms during the subsequent adhesive application processes. Such agglomeration may prevent the use of the individual forms, because it may be very difficult to remove the packaged hot-melt adhesive from the storage container, or it may prevent an automatic or semi automatic processing of the individual forms, e.g. pillows or prills, to be fed to the melting tanks. By automating this process, the customer will have significantly reduced handling and be able to store the adhesive at a further distance from the melt tank and convey with reduced operator requirement.
The packaging material of the hot-melt pressure sensitive adhesive typically includes various coating materials such as various portage linen blends and core polymers to avoid agglomeration. Currently, anti-blocking powders such as talc wax or silica are used in the discharge of hot-melts to avoid agglomeration. However, these compounds tend to become completely absorbed over time by the hot-melt and as a result, the residual tack reappears. Furthermore, some of the currently used anti-blocking agents such as silica dust are potentially harmful or can cause serious health issues, for example, lung or respiratory problems.
Packaged hot-melt pressure sensitive adhesives refer to adhesives, which form a bond when pressure is applied to attach the adhesives to the adhering substrates. Said pressure sensitive packaged adhesives are usually designed to properly attach to the adhering substrate at room temperature. Pressure sensitive adhesives have a tendency to fuse together at room temperature, which might lead to agglomeration of the pressure sensitive adhesive during normal handling and might therefore impair the use of the corresponding adhesives. To prevent such fusion and blocking of packaged hot-melt pressure sensitive adhesives, powder solutions are normally insufficient and said adhesives are typically packaged in more advanced coating material, e.g. a plastic or metal film.
U.S. Pat. No. 5,373,682 discloses a method for packaging hot-melt pressure sensitive adhesives into a plastic film. However, the method describes packaging a molten hot-melt adhesive into a solid plastic film and thereby does not disclosure a coextrusion process, wherein the adhesive composition and the coating are both applied in a molten state. A particular disadvantage of the process disclosed in U.S. Pat. No. 5,373,682 is that packaging of a molten hot-melt adhesive into a solid plastic film results in packaged adhesives, which are not uniformly packaged, e.g. which encompass air inclusions, which in turn may lead to an elevated blocking and fusion tendency of the packaged adhesives.
U.S. Pat. No. 7,572,494 B2 discloses a method for packaging hot-melt adhesives, in particular hot-melt pressure sensitive adhesives, which includes an extrusion process of a hot-melt adhesive and coextrusion of a wax-based polymeric film compositions to surround the hot-melt adhesive. However, the coextruded wax-based polymer coating consists of a polymer composition consisting of several different ingredients.
There remains a need in the art for packaged hot-melt pressure sensitive adhesives, which comprise anti-blocking coatings, which improve the handling of hot-melt adhesives and prevents agglomeration permanently and reliably.